Lens having at least one lens centration mark and methods of making and using same

ABSTRACT

A lens having at least one lens centration mark formed on a major surface of the lens is disclosed. The lens centration mark may be located at the intersection of a first axis and the major surface, where the major surface is symmetrical about the first axis such that the first axis is an axis of revolution of the surface. A method of making a lens having such lens centration mark, as well as a method for measuring the centration of a lens surface utilizing the lens centration mark, are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of prior U.S. ApplicationSer. No. 10/615,663, filed Jul. 9, 2003, now U.S. Pat. No. 6,951,392,the disclosure of which is herein incorporated by reference.

FIELD OF INVENTION

The present invention relates generally to the field of lenses, and inparticular to a lens having at least one centration mark and methods ofmaking and using same.

BACKGROUND

Optical elements often require testing to determine optical andmechanical characteristics. For example, it is often necessary to test alens for centration of one or both of a lens's surfaces.

Increasingly, lens designers have turned to aspherical surfaces to helpcontrol various types of optical aberrations that may occur in lenseshaving spherical surfaces. In general, an aspherical surface isconsidered to be shaped to a surface of revolution that is formed byrotating a non-circular curved shape about an axis of revolution. Thesurface of revolution is then rotationally symmetrical about the axis ofrevolution. Each aspherical surface that is a surface of revolutionincludes a vertex that is defined as the point on the surface where thesurface intersects the axis of revolution.

Aspherical lenses provide various advantages over more sphericalsurfaces. For example, an aspheric lens may have a much shorter focallength than is possible with a spherical lens of the same diameter. Thisshort focal length may be a useful feature where space is limited. Asingle aspherical lens may also be used as a condenser lens. Inmultilens systems, aspherics may help to correct aberrations.

Various improvements in lens design have also led to improvements inlens manufacturing as well. For example, injection molding of opticalgrade polymeric materials allows for the production of mass-producedhigh-quality optics that are made using lower-cost materials.

Plastic optics have a number of advantages over glass. Foremost of theseare lower cost, higher impact resistance, lighter weight, and moreconfiguration possibilities for simplifying system assembly.Configuration flexibility is especially useful in systems that useaspherical lenses to simplify system design and reduce parts count,weight, and cost. Moreover, light transmittance can be comparable tothat of high-grade crown glasses. Finally, the plastics that can breakgenerally do not splinter like glass. The fragments are larger and tendto be more obtuse and less hazardous.

Virtually all glass optic grinding and polishing equipment employsmechanisms that utilize mechanical movements for contouring sphericalsurfaces. Traditionally, finishing the optical pins of a mold forinjection and compression-molding has been performed with a similarprocess. Hence, most optics produced have been spherical.

However, optical designers are using aspheres increasingly to reducecosts or to obtain performance unavailable using other techniques.Designs using aspheres often contain fewer elements. Further, thecomplex process of producing a precise aspherical mold cavity surface isrequired only once for each cavity. Consequently, the injection moldingprocess is an economical technique for exploiting the advantages ofaspheres.

However, various errors can occur during injection molding of asphericallens surfaces that can produce surfaces that are decentered. Forexample, the optical axis of the surface may not be coincident with themechanical axis of the lens. For example, the two mold pins that make upan injection mold may not be properly aligned with each other such thatone or both lens surface's optical axes are not coincident with themechanical axis of the lens. In addition, the curable material used inthe injection molding process may unevenly shrink during curing.

SUMMARY

The present invention provides a lens that includes a first lenscentration mark located at a vertex of a major surface of the lens. Thefirst lens centration mark can allow for more accurate measurement ofthe centration of the major surface to the lens's mechanical axis. Insome embodiments of the present invention, the lens can also include asecond lens centration mark located on a second major surface of thelens.

The present invention further provides methods for measuring thecentration of a lens surface.

Among the advantages provided by some embodiments of the presentinvention is that a lens centration mark may be used with any shape ofoptical surface and provides an accurate and easily reproducible way ofmeasuring centration.

In one aspect, the present invention provides a lens having a firstmajor surface and a second major surface. The first major surface isrotationally symmetrical about a first axis. The first major surfaceincludes a first lens centration mark located at the intersection of thefirst major surface and the first axis. In some embodiments, the lensalso includes a second major surface of the lens that is rotationallysymmetrical about a second axis. The second major surface of the lensincludes a second lens centration mark located at the intersection ofthe second major surface and the second axis.

In another aspect, the present invention provides a method of forming alens centration mark on at least one surface of a lens. The methodincludes forming a first mold centration mark on a first surface of alens mold, where the first surface is rotationally symmetrical about afirst lens mold axis. The first mold centration mark is formed at theintersection of the first lens mold axis and the first surface of thelens mold. The method further includes filling the lens mold with acurable material, and curing the material such that the first moldcentration mark forms a first lens centration mark on a first majorsurface of the lens. In some embodiments, the method also includesforming a second mold centration mark on a second surface of the lensmold, where the second surface is rotationally symmetrical about asecond lens mold axis. The second mold centration mark is formed at theintersection of the second lens mold axis and the second surface of thelens mold. Curing the material further includes curing the material suchthat the second mold centration mark forms a second lens centration markon a second major surface of the lens.

In another aspect, the present invention provides a method of measuringcentration of a lens. The method includes placing the lens on a platen,where the lens includes a first major surface and a second majorsurface. The first major surface is rotationally symmetrical about afirst axis. The first major surface includes a first lens centrationmark located at the intersection of the first major surface and thefirst axis. Placing the lens on the platen includes placing the lens onthe platen such that the first lens centration mark is aligned with arotation axis of the platen. The method further includes leveling thelens relative to a plane of rotation that is orthogonal to the rotationaxis of the platen; rotating the lens about the rotation axis of theplaten; and observing the lens during or after rotation to assesscentration of the first major surface of the lens.

In some embodiments, the method further includes repositioning the lenson the platen such that a second lens centration mark on a second majorsurface of the lens is aligned with the rotation axis of the platen. Thesecond major surface of the lens is rotationally symmetrical about asecond axis. The second lens centration mark is located at theintersection of the second major surface and the second axis. The methodfurther includes rotating the lens about the rotation axis of theplaten, and observing the lens during or after rotation to assesscentration of the second major surface of the lens.

In another aspect, the present invention provides a method of measuringcentration of a lens. The method includes placing the lens on a platenin a first lens position, where the lens includes a first major surfaceand a second major surface. The first major surface is rotationallysymmetrical about a first axis. The first major surface includes a firstlens centration mark located at the intersection of the first majorsurface and the first axis. The method further includes determining afirst location of the first lens centration mark when the lens is in thefirst lens position; positioning the lens in a second lens position;determining a second location of the first lens centration mark when thelens is in the second lens position; and comparing the first location ofthe first lens centration mark and the second location of the first lenscentration mark.

In some embodiments, the method further includes determining a firstlocation of a second lens centration mark on a second major surface ofthe lens when the lens is in the first lens position, where the secondmajor surface of the lens is rotationally symmetrical about a secondaxis. The second lens centration mark is located at the intersection ofthe second major surface and the second axis. The method furtherincludes positioning the lens in the second lens position; determining asecond location of the second lens centration mark when the lens is inthe second lens position; and comparing the first location of the secondlens centration mark and the second location of the second lenscentration mark.

These and other features and advantages of lenses according to thepresent invention may be discussed below with respect to variousillustrative embodiments of the invention as defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view of one lens having a lens centrationmark according to the present invention.

FIG. 1B is a schematic cross section view of a portion of the lens ofFIG. 1B.

FIG. 2A is a schematic plan view of a lens having a first lenscentration mark and a second lens centration mark according to oneembodiment of the present invention.

FIG. 2B is a schematic cross section view of a portion of the lens ofFIG. 2A.

FIG. 3A is a schematic cross-section view of a lens mold apparatusincluding a lens mold according to one embodiment of the presentinvention.

FIG. 3B is a schematic cross-section view of the lens mold of FIG. 3A.

FIG. 4 is a schematic cross-section view of a mold pin having a moldcentration mark according to one embodiment of the present invention.

FIG. 5 is a schematic diagram of a centration measurement system formeasuring centration of a lens having at least one lens centration markaccording to one embodiment of the present invention.

FIG. 6 is a schematic top plan view of the lens of FIG. 5 shown inseveral rotated positions.

FIG. 7 is a schematic top plan view of one embodiment of the lens ofFIG. 5.

FIG. 8 is a schematic diagram of another centration measurement systemfor measuring centration of a lens having at least one lens centrationmark according to one embodiment of the present invention.

FIG. 9 is a schematic cross-section view of a lens having a first lenscentration mark and a second lens centration mark according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

In the following detailed description of illustrative embodiments,reference is made to the accompanying drawings that form a part hereof,and in which are shown, by way of illustration, specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

In general, the lenses of the present invention include at least onelens centration mark on a major surface of the lens.

As used herein, the term “aspherical lens” refers to a lens in which atleast one surface of the lens is shaped to a non-spherical surface ofrevolution about an axis of revolution.

As used herein, the term “vertex” refers to a point on a surface ofrevolution where the axis of revolution intersects the surface ofrevolution.

As used herein, the term “optical axis” refers to an axis that passesthrough the vertex of a lens surface and is coincident with the axis ofrevolution for that particular surface.

As used herein, the term “geometrical center of a lens” refers to theintersection of the midpoint of the diameter of a lens and the midpointof the thickness of the lens.

As used herein, the term “lens centration mark” refers to a mark orfeature formed in or on a surface of a lens such that the lenscentration mark is located at the intersection of the surface and theaxis of revolution of that surface. In other words, the lens centrationmark is located at the vertex of the surface of revolution.

As used herein, the term “decentration” refers to any lack ofcoincidence between the optical and mechanical axes. For a perfectlycentered lens surface, the mechanical axis of the lens is coincidentwith the optical axis. For surfaces having a lens centration mark,decentration of the surface would be indicated if the lens centrationmark is not aligned with the mechanical axis of the lens.

FIGS. 1A-1B illustrate one embodiment of a lens 10 according to thepresent invention. Lens 10 includes a first major surface 12, a secondmajor surface 20, and an outer edge 14. The first major surface 12includes a lens centration mark 30 as further described herein. The lenscentration mark 30 is not made to scale in FIGS. 1A-1B for illustrativepurposes. Lens 10 may be any suitable type of lens known in the art,e.g., plano-convex, double convex, meniscus, plano-concave, doubleconcave, or aspherical. Further, the lens 10 may be used in any numberof types of devices and for various types of optical effects, e.g.,microscopes, cameras, telescopes, projection televisions, glasses, datadisplay projectors, and video display projectors.

The lens 10 may be made of any suitable material or combination ofmaterials, e.g., glass, polymeric, or crystalline. Further, lens 10 mayinclude various materials in the lens 10 or as coatings for providingvarious optical properties, e.g., anti-reflective, anti-scratch,anti-stain, etc.

Lens 10 may be any suitable size depending on its particular use. Forexample, 10 mm diameter lenses can be useful for some camera orprojection lens assemblies. Alternatively, lenses that are approximately200 mm in diameter can be useful for some television lens assemblies.

The outer edge 14 of lens 10 may take any suitable shape, e.g.,circular, rectangular, etc. Further, the outer edge 14 may include oneor more gate protrusions from the injection molding process (see, e.g.,gate protrusion 418 of lens 410 of FIG. 7). In addition, lens 10 mayinclude integral mounting and fastening features proximate the outeredge 14 for mounting the lens 10 in an optical assembly. For example,such fastening features may include square flanges, protrusions for heatstaking, holes with mounting pads, etc. Further, lens 10 may includemounting flats for mounting in an optical assembly.

As mentioned above, lens 10 includes a first major surface 12, which maytake any suitable shape depending upon the desired optical properties ofthe lens 10. For example, first major surface 12 may be convex, concave,or planar. Further, a convex or concave surface may take a spherical oraspherical shape. It may be preferred that first major surface 12 isgenerally symmetrical about a first axis 50. In other words, first majorsurface 12 may be described by rotating a selected non-circular curveabout first axis 50 to form a surface of revolution. In the illustratedembodiment, the first axis 50 is an axis of revolution for describingthe first major surface 12. In general, aspherical surfaces can bedescribed as surfaces of revolution that are rotationally symmetricalabout an axis of revolution. As illustrated in FIG. 1A, vertex 52indicates where the first axis 50 (i.e., the axis of revolution for thefirst major surface 12) intersects the first major surface 12 (i.e., thesurface of revolution).

Opposed from the first major surface 12 of lens 10 is the second majorsurface 20, which can take any suitable shape depending upon the desiredoptical properties of lens 10, e.g., convex, concave, planar. Further, aconvex or concave surface may take a spherical or aspherical shape. Aswith the first major surface 12, the second major surface 20 may also bedescribed as a surface of revolution.

The first major surface 12 includes a first lens centration mark 30. Asillustrated in the figures of the present invention, lens centrationmarks are not drawn to scale for ease of illustration. The first lenscentration mark 30 may be located at the intersection of the first majorsurface 12 and the first axis 50, i.e., at the vertex 52 of the firstmajor surface 12. As used herein, the term “at” as used, e.g., in thephrase “located at the intersection of the first major surface 12 andthe first axis 50” means that the first lens centration mark 30 islocated exactly at the intersection of the first axis 50 and the firstmajor surface 12 or within a required tolerance. The amount of tolerancewill depend on the lens diameter. For example, a 200 mm lens with 25 μmtolerance is about 0.01% tolerance.

The first lens centration mark 30 may take any suitable shape, e.g.,circular, triangular, rectangular, etc. Further, the first lenscentration mark 30 may be any discontinuous arrangement of markings(e.g., cross-hair markings, bumps) having generally sharp edges suchthat the mark 30 may be distinguished from various lens defects.Further, the first lens centration mark 30 may be of any suitable size,i.e., height and diameter. For example, the first lens centration mark30 may be less than 25 μm in height (or depth if mark 30 extends intothe first major surface 12). It may be preferred that the first lenscentration mark 30 may be less than 1 μm in height. Further, forexample, the first lens centration mark 30 may be no more than 100 μm indiameter. It may be preferred that the first lens centration mark 30 isno more than 50 μm in diameter. It may be more preferred that the firstlens centration mark 30 is no more than 25 μm in diameter.Alternatively, it may be preferred that the first lens centration mark30 is smaller than various allowed defects, such as scratches or digs,for the particular lens's specifications. Further, it may be preferredthat the first lens centration mark 30 does not substantially affect theoptical performance of lens 10, while the first lens centration mark 30is still of sufficient size such that a microscope can be focused ontomark 30 and be centered in the microscope's crosshairs as is furtherdescribed herein. Further, it may be preferred that the lens centrationmark 30 have a sharp edge such that a microscope or other optical devicemay more easily focus on the lens centration mark 30.

Although the first lens centration mark 30 is depicted in FIG. 1A asbeing a bump or protuberance that extends from the first major surface12, the first lens centration mark 30 may also be a depression or dimpleextending into the first major surface 12, or some combination ofprotruberance and depression.

The first lens centration mark 30 may be formed using any suitabletechnique known in the art. For example, the first lens centration mark30 may be formed by engraving a corresponding mold centration mark on asurface of a mold pin used in an injection molding process as furtherdescribed herein. Alternatively, the first lens centration mark 30 canbe formed by embossing the first major surface 12 of lens 10. Further,for example, the first lens centration mark 30 may be formed byattaching the first lens centration mark 30 to the first major surface12 of lens 10, e.g., by bonding the first lens centration mark 30 to thefirst major surface 12. Other techniques may include diamond turning,laser ablation, spot coating, etc.

Because it is located at the vertex 52 of the first major surface 12 oflens 10 (i.e., at the intersection of the first axis 50 and the firstmajor surface 12), the first lens centration mark 30 along with thefirst axis 50 indicate the optical axis of the first major surface 12.As is further described herein, it is generally desirable that theoptical axis of each surface of a lens be substantially coincident withthe mechanical axis of the lens. By providing the first lens centrationmark 30 on the first major surface 12 of lens 10, the centration of thefirst major surface 12 with the mechanical axis of the lens 10 may bedetermined.

Although lens 10 illustrated in FIGS. 1A-1B includes a first lenscentration mark 30, the lenses of the present invention may also includea second lens centration mark on a second major surface of the lens. Forexample, FIG. 9 illustrates lens 600 having a first lens centration mark630 and a second lens centration mark 640 according to anotherembodiment of the present invention. Lens 600 exhibits several featuresthat are similar to those of lens 10 illustrated in FIGS. 1A-1B anddescribed herein. Lens 600 includes a first major surface 612, a secondmajor surface 620, and an outer edge 614. Lens 600 may be made of thesame or similar materials as those used to manufacture lens 10.

Both the first and second major surfaces 612 and 620 may include anysuitable shape known in the art, e.g., convex, concave, or planar. Forconvex and concave shapes, the first and second major surfaces 612 and620 may take any suitable shape, e.g., spherical, or aspherical. Asillustrated in FIG. 9, first major surface 612 is rotationallysymmetrical about an axis 670. In other words, first major surface 612may be described by rotating a non-circular curve about axis 670 (i.e.,the axis of revolution) to form a surface of revolution. Axis 670intersects the first major surface 612 at vertex 652.

In the embodiment illustrated in FIG. 9, the second major surface 620 isalso rotationally symmetrical about axis 670 such that the second majorsurface 620 is a surface of revolution about axis 670 (i.e., the axis ofrevolution). The axis 670 intersects the second major surface 620 atvertex 662.

In the embodiment illustrated in FIG. 9, lens 600 has a diameter d, themidpoint of which, along with the midpoint of the distance between thefirst major surface 612 and the second major surface 620, define thegeometrical center 672 of the lens 600. The geometrical center 672 inturn defines the mechanical axis, which is an axis that is orthogonal tothe lens diameter d and intersects the geometrical center 672 of lens600. In this embodiment, the mechanical axis is coincident with axis670.

As illustrated in FIG. 9, the axes of revolution of the first majorsurface 612 and second major surface 620 are coincident with themechanical axis of the lens 600 such that all three axes are depicted asaxis 670. In an ideal lens, it may be preferred that these three axesare coincident such that the lens does not exhibit decentration. Inother words, it may be preferred that the first lens centration mark 630and the second lens centration mark 640 are both aligned with themechanical axis of the lens (i.e., axis 670).

However, some lenses may exhibit decentration of at least one lenssurface. For example, FIGS. 2A-2B illustrate another embodiment of alens 100 according to the present invention. Lens 100 is similar in manyrespects to lens 10 of FIGS. 1A-1B and lens 600 of FIG. 9. Lens 100includes a first major surface 112, a second major surface 120, and anouter edge 114.

As illustrated in FIG. 2B, first major surface 112 is rotationallysymmetrical about a first axis 150. In other words, first major surface112 may be considered to be a surface of revolution described byrotating a non-circular curve about first axis 150 (i.e., the axis ofrevolution). First axis 150 intersects the first major surface 112 atvertex 152.

Similarly, as illustrated in FIG. 2B, the second major surface 120 issymmetrical about a second axis 160 such that second major surface 120is a surface of revolution. Second axis 160 intersects the second majorsurface 120 at vertex 162.

Located at the intersection of the first axis 150 and the first majorsurface 112 (i.e., at the vertex 152) is a first lens centration mark130. As described herein with reference to first lens centration mark 30of FIGS. 1A-1B, first lens centration mark 130 may be any suitable shapeand size. It may be preferred that first lens centration mark 130 is ofa size such that it does not substantially affect the optical propertiesof the lens 100. The first lens centration mark 130 may be used todetermine the centration of the first major surface 112 of lens 100 asis further described herein.

Lens 100 further includes a second lens centration mark 140 located atthe intersection of the second axis 160 and the second major surface 120(i.e., at vertex 162). As stated in regard to the first lens centrationmark 30 of FIGS. 1A-1B, the second lens centration mark 140 can take anysuitable shape and size. The second lens centration mark 140 can be usedto determine the centration of the second major surface 120 of lens 100as is further described herein.

FIG. 2A is a schematic plan view of the lens 100 looking down on thefirst major surface 112. Although FIG. 2A shows the first lenscentration mark 130 as being non-aligned with the second lens centrationmark 140 along an axis orthogonal to the plane of FIG. 2A, the firstlens centration mark 130 and the second lens centration mark 140 may bealigned such that the first axis 150 and the second axis 160 of FIG. 2Bare coincident (see, e.g., lens 600 of FIG. 9).

Lens 100 further includes a geometrical center 172 that, in turn,defines the mechanical axis 170, which is an axis that is orthogonal tothe lens diameter and intersects the geometrical center 172.

In an ideal lens, it may be preferred that the first lens centrationmark 130 of the first major surface 112 and the second lens centrationmark 140 of the second major surface 120 both are aligned with themechanical axis 170 of the lens 100. Such alignment may ensure that theoptical axis (i.e., first axis 150 and second axis 160) is coincidentwith the mechanical axis 170. In a system of one or more lenses,alignment of the surfaces of each lens may help to reduce imageprocessing errors, such as coma, astigmatism, field tilt, decentration,and other aberrations known in the art.

In some embodiments of the present invention, the centration of thefirst major surface 112 can be compared to the centration of the secondmajor surface 120 to determine the curve to curve decentration of lens100. This curve to curve decentration can be determined using anysuitable technique.

Errors may occur during the manufacturing of a lens that causes one orboth surfaces of a lens to become decentered from the lens's mechanicalaxis. For example, both the first major surface 112 and the second majorsurface 120 of lens 100 are decentered from the mechanical axis 170. Itmay be preferred that the lenses of the present invention have at leastone lens surface that is centered along the lens's mechanical axis. Itmay be more preferred that both surfaces of a lens of the presentinvention be centered along the lens's mechanical axis. In other words,it may be preferred that the first axis 150 (i.e., the optical axis) ofthe first major surface 112 is substantially coincident with themechanical axis 170 of lens 100. Similarly, it may be preferred that thesecond axis 160 is substantially coincident with the mechanical axis170. It may be more preferred that both the first axis 150 and thesecond axis 160 are substantially coincident with the mechanical axis170. In other words, it may be preferred that the first lens centrationmark 130 and the second lens centration mark 140 are aligned with themechanical axis 170.

In FIG. 2B, the first major surface 112 is decentered such that thefirst axis 150 (i.e., the axis of revolution of the first major surface112) is not coincident with the mechanical axis 170. Because the firstlens centration mark 130 is located at the vertex 152 of the first majorsurface 112, the total distance 180 that the first major surface 112 isdecentered from the mechanical axis 170 can be measured from the centerof the first lens centration mark 130 (i.e., the vertex 152) to themechanical axis 170. This distance 180 is the decentration of the firstmajor surface 112. Similarly, the decentration 182 of the second majorsurface 120 can be measured from the center of the second lenscentration mark 140 (i.e., the vertex 162) to the mechanical axis 170.As previously described, it may be preferred that the decentration 180and 182 of both the first and second major surfaces 112 and 120 be assmall as possible to reduce the likelihood of optical aberrations causedby decentration.

The lenses described herein can be made of any suitable materials andmanufactured using any suitable techniques. It may be preferred that thelenses utilized with the methods of the present invention be made ofpolymeric material or materials and manufactured using an injectionmolding process. One embodiment of an apparatus for injection moldinglenses is described in reference to FIGS. 3A-3B. Generally, an apparatus200 for injection molding lenses includes a mold 210 placed between twoplatens 250 that press the mold 210 together with the aid of a clampingunit 252. A curable material 272 in raw form is fed into a hopper 270,which feeds the material into an injection unit 260. Heat bands 262,which surround the injection unit 260 heat the curable material 272until it is in molten form 274. The injection unit 260 injects themolten material 274 into the mold 210.

The mold 210 includes one or more mold pins 220. Each mold pin 220includes a mold surface 222 that is shaped to form the desired type oflens surface. For example, for aspherical lenses, the mold surface 222may include an aspherical surface described by rotating a curve about anaxis of revolution 240. After the injection unit 260 injects the moltenmaterial 274 into the mold 210, the molten material 274 is cured to formlens 230. Although FIGS. 3A-3B depict one general embodiment of anapparatus and technique for injection molding a lens, those skilled inthe art will understand that the lenses and methods of forming and usingsuch lenses described herein can be made using any suitable techniqueknown in the art.

FIG. 4 is a cross-section view of one mold pin 300 according to oneembodiment of the present invention. Mold pin 300 may be used with anysuitable injection molding apparatus known in the art, e.g., apparatus200 of FIG. 3A. The mold pin 300 includes a first mold pin surface 310that is rotationally symmetrical about a first mold pin axis 350. Themold pin 300 may be manufactured using any suitable material ormaterials, e.g., steel, aluminum, nickel, stainless steel, copperalloys, etc. The first mold pin surface 310 may be any suitable shapefor forming a desired type of lens, e.g., convex, concave, or planar.Further, convex and concave surfaces may take spherical or asphericalshapes.

The first mold pin surface 310 includes a vertex 352 that is the pointat which the first mold pin axis 350 intersects the outline of the firstmold pin surface 310. The first mold pin surface 310 also includes afirst mold centration mark 330 formed at the vertex 352. The first moldcentration mark 330 may include any suitable shape, e.g., circular,triangular, rectangular. Further, the first mold centration mark 330 canbe a bump or protuberance that extends from the first mold pin surface310. Alternatively, the first mold centration mark 330 can be a dimpleor depression that extends into the first mold pin surface 310. Thefirst mold centration mark 330 is generally the reverse image of thelens centration mark to be formed on a surface of a lens that is to bemanufactured using the mold pin 300 (e.g., first lens centration mark 30of lens 10 of FIGS. 1A-1B).

The first mold centration mark 330 may be formed using any suitabletechnique known in the art, e.g., engraving, embossing, etching, laserablation, vacuum coating, etc. It may be preferred that the first moldcentration mark 330 is formed by engraving. For example, the mold pin300 can be placed on a rotating chuck and rotated as the first surface310 is contacted with an engraving tool, e.g., a diamond tipped probe,tool steel, cubic boron nitride, etc.

In an injection molding process, one or both mold pins can have a moldcentration mark formed on the pin's surface at its vertex.

Several methods can be used to measure the centration of one or moresurfaces of the lens. FIG. 5 is a schematic diagram of one embodiment ofa centration measurement system 400 according to the present invention.The system 400 includes a platen 440 that rotates about a rotation axis442. The platen 440 may rotate either clockwise or counterclockwise. Alens 410 (e.g., lens 100 of FIG. 2A) is placed on platen 440 such thatboth the platen 440 and the lens 410 rotate about the rotation axis 442.

The lens 410 may be similar to other lenses described herein. The lens410 includes a first major surface 412, a second major surface 420, anouter edge 414, and a geometrical center 416. Further, the first majorsurface 412 includes a first lens centration mark 430 at a vertex (notshown) of the first major surface of the lens 410. Although depicted ashaving only a first lens centration mark 430, the lens 410 may furtherinclude a second lens centration mark on the second major surface 420 asfurther described herein (e.g., second lens centration mark 140 of lens100 of FIGS. 2A-2B).

Adjacent the platen 440 is a moment indicator 450. The moment indicator450 may be any suitable indicator, e.g., the Formscan 3100 made by MahrFederal (Providence, R.I., USA). The moment indicator 450 is operable tomeasure runout of the lens 410 as the lens 410 and platen 440 rotate.For example, the moment indicator 450 may include a spring-loaded probethat contacts the lens 410 and detects movement of the lens 410 in aplane of rotation 444 as the lens 410 rotates.

The system 400 further includes a microscope 460 including a lightsource 470. The microscope 460 may be any suitable microscope, e.g., a100 power microscope having an eyepiece with a cross-hair. Further, thelight source 470 may be any suitable light source for illuminating thelens 410 for viewing in the microscope 460, e.g., a ¼ inch fiber opticbundle with a fiber optic illuminator. Together, the microscope 460 andthe light source 470 are operable to focus on the first lens centrationmark 430 of the first major surface 412 of the lens 410. Further, if thelens 410 includes a second lens centration mark on the second majorsurface 420, then the microscope 460 is operable to focus through lens410 and onto the second lens centration mark. The microscope 460 ispositionable such that it is aligned along the rotation axis 442 ofplaten 440. The microscope 460 may also include an indicator (not shown)that is operable to measure the distance the microscope travels in aplane parallel to the plane of rotation 444 as is further describedherein.

A method for measuring the centration of a lens including at least onelens centration mark will now be described in reference to FIGS. 5-7.Lens 410, which includes first lens centration mark 430 on first majorsurface 412, is placed on the platen 440. The lens 410 is leveledrelative to the plane of rotation 444. The plane of rotation 444 isorthogonal to the rotation axis 442. The lens 410 may be leveled usingany suitable technique known in the art. Further, the platen 440 mayinclude a mechanism for aiding in leveling the lens 410 on the platen440. Further, the apparatus 400 may include a controller and softwarethat aid in leveling and centering lens 410 on platen 440.

The lens 410 is placed such that the first lens centration mark 430 isaligned with the rotation axis 442 of the platen 440. Any suitabletechnique of placing the first lens centration mark 430 on the rotationaxis 442 may be utilized. For example, the lens 410 may be placed on theplaten 440 and the platen 440 rotated while the lens 410 is observedthrough the microscope 460. If the first lens centration mark 430 isaligned with the rotation axis 442, then the mark 430 will remainsubstantially stationary in the plane of rotation 444 as the lens 410and platen 440 rotate. If, however, the first lens centration mark 430does not remain stationary, then the lens 410 is repositioned on theplaten 440 and once again the lens 410 and platen 440 are rotated as thelens 410 is observed through the microscope 460. This process may berepeated any number of times until the first lens centration mark 430remains stationary in the plane of rotation 444 as the lens 410 andplaten 440 are rotated.

Once the lens 410 is leveled, the lens 410 and platen 440 are rotatedabout the rotation axis 442. As the lens 410 and platen 440 rotate, thelens 410 is observed to assess centration of the first major surface 412of the lens 410. For example, the moment indicator 450 may measure adistance that the lens 410 travels in the plane of rotation 444 as thelens 410 rotates. This distance can be referred to as the TotalIndicated Runout (TIR). If the vertex (indicated by the first lenscentration mark 430) is aligned with the mechanical axis of the lens 410(e.g., mechanical axis 170 of FIG. 2B), then the lens 410 will nottravel back and forth in the plane of rotation 444 while the lens 410rotates. In other words, if the axis of revolution (i.e., the opticalaxis) of the first major surface 412 and the mechanical axis aresubstantially coincident, then both the axis of revolution of the firstmajor surface 412 and the mechanical axis are substantially coincidentwith the rotation axis 442, and the lens 410 will rotate about therotation axis 442 without any runout.

If, on the other hand, the axis of revolution of the first major surface412 of lens 410 is not substantially coincident with the mechanicalaxis, then the mechanical axis will rotate around the rotation axis 442as the lens 410 rotates, and the outer edge 414 of the lens 410 willmove back and forth in the plane of rotation 444, i.e., the lens 410will exhibit runout. For example, in FIG. 6, the lens 410 is pictured atvarious positions in its motion about the rotation axis 442. Lens 410 aillustrates lens 410 at a time T₁. At time T₁, lens 410 a includes firstlens centration mark 430 and geometrical center 416 a. At time T₂, thelens 410 b has traveled such that outer edge 414 b is a distance 480from a reference point 452. The reference point 452 may be a point fixedon the moment indicator 450. At time T₂, the geometrical center hasmoved from center 416 a to center 416 b while the first lens centrationmark 430 has remained fixed because the first lens centration mark 430is aligned with the rotation axis 442. At time T₃, the lens 410 c hasrotated clockwise from its position at T₂, such that the outer edge 414c of lens 410 c is a distance 482 from reference point 452. Thegeometrical center of lens 410 has moved from center 416 b to center 416c. This movement of the geometrical center as lens 410 rotates indicatesthat the mechanical axis is rotating around the rotation axis 442. Thismovement of the geometrical center 416 as well as the outer edge 414 ofthe lens 410 indicates that the first major surface 412 of lens 410 isdecentered from the mechanical axis of the lens.

As illustrated in FIG. 6, distance 480 is the minimum distance from theedge 414 of lens 410 to reference point 452, and distance 482 is themaximum distance from edge 414 to reference point 452. The totalindicated runout (TIR) of the lens 410 may be determined by comparingthe maximum distance 482 with the minimum distance 480 using anysuitable technique known in the art. For example, the minimum distance480 may be subtracted from the maximum distance 482 to provide TIR 484.To determine the amount of decentration, the TIR is divided in half.This provides the runout of the first major surface 412 of lens 410.

The above-described method may also be used to determine the directionof the decentration such that adjustments may be made to the mold. Forexample, FIG. 7 illustrates another embodiment of lens 410 of FIGS. 5-6,where lens 410 further includes a gate protrusion 418. The gateprotrusion 418 is formed from the gate on the injection mold apparatuswhen the lens 410 is manufactured. The gate protrusion 418 may be usedas a reference mark to determine the direction in which the lens 410 mayhave become decentered. Although the gate protrusion 418 may be used asa reference, other techniques of defining a reference may be used.

As the lens 410 and platen 440 are rotated, the operator determines thelocation of the gate protrusion 418 and sets that as a reference. Themoment indicator 450 then determines the direction of the runout fromthe position of the gate protrusion 418 when the lens is at either themaximum distance 482 or the minimum distance 480 from the referencepoint 452.

After determining the runout and location of runout of lens 410, thecentration of the second major surface 420 can be determined using asecond lens centration mark that is located on the second major surface420 (e.g., the second lens centration mark 140 of lens 100 of FIGS.2A-2B). The microscope 460 is focused through the first major surface410 of lens 400 and onto the second lens centration mark on the secondmajor surface 420 and the second lens centration mark is positioned suchthat it is on the rotation axis 442. The above-mentioned method is thenrepeated to determine the runout of the second major surface 420 of lens410. Further, the direction of the runout of the second major surface420 may also be determined using the techniques described herein.

Another method for determining the centration of one or more surfaces ofa lens having at least one lens centration mark will now be described inreference to FIG. 5. The lens 410 is centered on the platen 440 suchthat a geometrical center 416 of the lens is aligned with the rotationaxis 442. Any suitable technique may be used to mechanically center thelens on the platen 440. For example, U.S. Pat. No. 5,835,208 describes amethod for mechanically centering a lens. The microscope 460 is focusedon the first lens centration mark 430 such that crosshairs of themicroscope 460 are centered on the mark 430. The platen 440 and lens 410are rotated until the lens 410 is in a first lens position. If the firstmajor surface 412 is decentered, then the first lens centration mark 430will runout in a circular orbit around the rotation axis 442 as the lens410 and platen 440 are rotated. An indicator in communication with themicroscope 460 (not shown) is set to zero. The lens 410 and platen 440are rotated to a second lens position such that the lens 410 rotatesapproximately 180 degrees from the first lens position. The microscope460 is moved from the previous position until its crosshairs are onceagain centered on the first lens centration mark 430. The microscope'stravel distance between the first lens position and second lens positionis determined using the indicator. This distance is the TIR for thefirst major surface 412 of the lens 410. The microscope 460 may then befocused through the first major surface 412 to a second lens centrationmark on the second major surface 420 to determine the centration of thesecond major surface 420 using the above-described method or any othersuitable technique known in the art.

FIG. 8 is a schematic diagram of another embodiment of a lens centrationsystem 500 according to the present invention. Lens centration system500 is similar to lens centration system 400 of FIG. 5. For example,lens centration system 500 includes platen 590. A lens 510 having atleast one lens centration mark 530 may be placed on a surface 596 of theplaten 590. The system 500 further includes a microscope 560 and a lightsource 570.

In communication with microscope 560 is an optical coordinate measuringmachine (CMM) 580. The CMM 580 may be any suitable CMM known the art,e.g., the Avant Apex video measuring system manufactured by OpticalGaging Products, Inc. (Rochester, N.Y., USA). The CMM 580 is operable tocommunicate with microscope 560 such that the CMM 580 can determine thecoordinates of one or more locations on a surface. Any suitablecoordinate system may be used, e.g., Cartesian, polar, etc. The CMM 580may include a controller and software for controlling the microscope 560and determining such coordinates of one or more locations.

A method of measuring the centration of a lens will now be described inreference to FIG. 8. Lens 510 is placed on the surface 596 of the platen590 in a first lens position such that the first lens centration mark530 is facing the microscope 560. The lens 510 can be placed such thatits geometrical center is centered on the platen 590. It may bepreferred that the lens 510 is centered on the platen 590 such that thegeometrical center of the lens 510 can be used as a reference indetermining the locations of the first lens centration mark 530 asdescribed herein. The lens 510 can be centered on the platen 590 usingthe lens's mounting surfaces, which may be the lens's diameter andeither a second major surface 520 of lens 510 or an edge flat 518 of thelens 510. The diameter of lens 510 can be located by placing the lensagainst post 592. Although only one post 592 is illustrated in FIG. 8,two or more posts 592 may be utilized to center lens 510 on platen 590.Further, any suitable posts or other device for locating the diameter ofthe lens 510 may be used. Alternatively, if the second major surface 520of lens 510 is the mounting surface, then the lens 510 can be placed onposts 594 such that lens 510 is level in relation to platen 590.Although system 500 utilizes either posts 592 or 594 to center lens 510on platen 590, any suitable technique or device may be used to centerlens 510.

The CMM 580 determines a first location of the first lens centrationmark 530 in this first lens position. In other words, the CMM 580determines the coordinates (e.g., Cartesian, polar, etc.) of the firstlens centration mark 530 in the first lens position and stores suchcoordinates for later reference. The microscope 560 may be used to aidthe CMM 580 in determining the first location of the first lenscentration mark 530 by focusing the microscope 560 onto the mark 530.

The lens 510 is then positioned in a second lens position. It may bepreferred that the second lens position is an approximately 180 degreerotation of the lens 510 about the geometrical center of the lens 510such that the lens 510 is centered on the platen 590.

After the lens 510 is positioned in the second lens position, the CMM580 determines a second location of the first lens centration mark 530by finding the coordinates of the first lens centration mark 530. Thissecond location is compared to the first location to determine the TIRof the first major surface 512 of lens 510 using any suitable techniqueknown in the art. If the first lens centration mark 530 is aligned withthe mechanical axis of the lens 510, then the first location and thesecond location of the first lens centration mark 530 should besubstantially identical. In other words, the coordinates of the firstlens centration mark 530 in the first lens position and the coordinatesof the first lens centration mark 530 in the second lens position shouldbe substantially the same. However, if these two sets of coordinates aredifferent, then the CMM 580 determines the TIR of the first majorsurface 512 using techniques known the art. Further, the CMM 580 isoperable to determine the direction of any TIR of the first majorsurface using any suitable technique further described herein.

The centration of the second major surface 520 can also be measuredusing the above-described techniques. In some embodiments, thecoordinates of both the first lens centration mark 530 and a second lenscentration mark 540 can be determined while the lens 510 is in the firstlens position, and then the coordinates of marks 530 and 540 can bedetermined when the lens 510 is in the second lens position.

Although the methods described above are applied to a single lens, suchmethods may also be used to determine the centration of two or morelenses in an optical assembly relative to the mechanical axis of theassembly. For example, a microscope with a long working distanceobjective may be used to focus through the two or more lenses of theassembly. The assembly is mounted on an adjustable stage so that themechanical axis or the optical axis of each lens is coincident with theaxis of the microscope. If a lens is decentered, then that particularlens's centration mark will be displaced from the cross-hair of themicroscope.

All references and publications cited herein are expressly incorporatedherein by reference in their entirety into this disclosure. Illustrativeembodiments of this invention are discussed and reference has been madeto possible variations within the scope of this invention. These andother variations and modifications in the invention will be apparent tothose skilled in the art without departing from the scope of theinvention, and it should be understood that this invention is notlimited to the illustrative embodiments set forth herein. Accordingly,the invention is to be limited only by the claims provided below.

1. A lens comprising a first major surface and a second major surface, wherein the first major surface is rotationally symmetrical about a first axis, wherein the first major surface comprises a first lens centration mark located at the intersection of the first major surface and the first axis, the first lens centration mark defining one of a protuberance and a depression, and wherein the second major surface of the lens is rotationally symmetrical about a second axis, and further wherein the second major surface of the lens comprises a second lens centration mark located at the intersection of the second major surface and the second axis.
 2. The lens of claim 1, wherein the first lens centration mark comprises a diameter of no more than 50 μm.
 3. The lens of claim 1, wherein the lens further comprises a polymeric material.
 4. The lens of claim 1, wherein the first major surface of the lens comprises a spherical shape.
 5. The lens of claim 1, wherein the first major surface of the lens comprises an aspherical shape.
 6. The lens of claim 5, wherein the second major surface of the lens comprises an aspherical shape.
 7. The lens of claim 1, wherein the second major surface of the lens comprises a planar shape.
 8. The lens of claim 1, wherein the lens further comprises a mechanical axis, and further wherein the first lens centration mark is aligned with the mechanical axis.
 9. The lens of claim 8, wherein the second lens centration mark is aligned with the mechanical axis.
 10. The lens of claim 1, wherein the lens further comprises a mechanical axis, and further wherein the first lens centration mark is aligned with the mechanical axis.
 11. A lens comprising a first major surface and a second major surface, wherein the first major surface is rotationally symmetrical about a first axis, the first axis being different from an optical axis of the lens, wherein the first major surface comprises a first lens centration mark located at the intersection of the first major surface and the first axis, wherein the second major surface of the lens is rotationally symmetrical about a second axis, and further wherein the second major surface of the lens comprises a second lens centration mark located at the intersection of the second major surface and the second axis.
 12. The lens of claim 11, wherein the first major surface of the lens comprises a spherical shape.
 13. The lens of claim 11, wherein the first major surface of the lens comprises an aspherical shape.
 14. The lens of claim 13, wherein the second major surface of the lens comprises an aspherical shape.
 15. The lens of claim 11, wherein the second major surface of the lens comprises a planar shape.
 16. The lens of claim 11, wherein the lens further comprises a mechanical axis, and further wherein the first lens centration mark is aligned with the mechanical axis.
 17. The lens of claim 16, wherein the second lens centration mark is aligned with the mechanical axis.
 18. The lens of claim 11, wherein the first axis is arranged noncoaxial with the optical axis.
 19. A lens comprising a first major surface and a second major surface, wherein the first major surface is rotationally symmetrical about a first axis, wherein the first major surface comprises a first lens centration mark located at the intersection of the first major surface and the first axis, wherein the second major surface of the lens is rotationally symmetrical about a second axis, and further wherein the second major surface of the lens comprises a second lens centration mark located at the intersection of the second major surface and the second axis.
 20. The lens of claim 19, wherein the lens further comprises a mechanical axis, and further wherein the first lens centration mark is aligned with the mechanical axis.
 21. The lens of claim 20, wherein the second lens centration mark is aligned with the mechanical axis. 